The present invention relates to improved axially-flexible metal bellows for use in heat-sensitive and/or pressure-sensitive devices, such as valves. Conventional metal bellows devices are formed by superposing or stacking a pile of similar flexible diaphragms comprising metal annuli free plates or rings and welding or soldering the inner and outer peripheries of alternate free plates or rings to each other to form fluid-tight welds. The top and bottom free plates are soldered or welded to fittings of a valve or other device to form a closed, fluid-tight interior compartment and/or a closed fluid-tight exterior compartment, the latter being formed between the outside of the bellows and a sealed casing of the valve or other device. Pressure variations between the interior and the exterior of the bellows cause axial expansion or contraction of the accordion-like bellows, which movement is adapted to activate a component, such as cause a valve member to close or open, as desired, to relieve the conditions giving rise to the excess pressure or temperature conditions.
Reference is made to U.S. Pat. Nos. 3,394,631 and 3,503,770 for their disclosure of bellows devices and the problems involved therewith.
The bellows devices of the present invention are of the type formed by welding together a plurality of superposed or stacked flexible metal annuli or rings, the inner and outer peripheries of alternate adjacent annuli or rings being welded or soldered together to form an accordion-like, axially-flexible bellows in which the joined annuli or rings flex together or away from each other in response to changes in internal or external pressures. A reduced internal pressure or increased external pressure causes the annuli or rings, referred to as free plates, to flex together to retract the bellows and the valve member associated therewith. Since the peripheral welds which unite the flexible thin free plates are substantially thicker than the plates themselves, such retraction causes the peripheral welds to be compressed against each other under substantial pressure each time the bellows retracts. Also, the free plates try to flex into intimate surface contact with each other in the areas adjacent the welds each time the bellows retracts. Such repeated action can result in damage to the integrity of the welds and/or cracking of the thin flexible free plates, whereby the fluid-impermeability of the bellows is lost and the bellows must be replaced.